Radio direction finder



June 10, i947. D. s. Bom 2,422,073

RADIO DIRECTION FINDER nnentor Gttorneg June 10,1947. n.5. BOND 2,422,073

v v RADIO DIRECTION FINDER Filed 4July 5o, 1942 2 sheets-sheet 2 nu uA "wr uw n (lttorneg Patented June 10, 1947 RADIO vDIRECTION FINDER,

Donald S. Bond, Philadelphia, Pa., assignor 'to Radio Corporation of America, a corporation of Delaware Application July 30, 1942, Serial No. 452,825

(Cl. Z50-11) Claims.

This invention relates to radio direction finders of the stationary antenna, direct indicating type. Two similar directive antennas or arrays are positioned with their directivity patterns at right angles to each other. The two antenna outputs are amplified, detected, and applied to reotangularly disposed deecting elements in a bearing indicator, which operates continuously to show the instantaneous azimuth of arrival of waves to which the apparatus is tuned.

Although it is possible to use separate receivers for each of the two antennas, such an arrangement requires identical gains through the two channels in order to give accurate bearing indications. 'I'he equality of gain required is far beyond the capacity of conventional automatic gain control systems.

In order to avoid errors due to different treatment of the signals from the two antennas, it is desirable to combine the signals before amplification, employ a common ampliiier, and then separate the components corresponding to the original signals. According to the present invention, the antenna outputs are diiierently modulated, amplied and detected together, and the products separated by means responsive to the respective modulations.

The principal object of this invention is to provide an improved xed antenna direct indicating direction iinder system.

Another object is to provide an improved method of and means for amplifying thev individual antenna signals in a system of the described type.

A further object is to provide an improved method of and means for deriving two voltages of vthe same low frequency, with amplitudes proportional to the respective signals picked up by each of a pair of antennas.

Other and incidental objects of the invention will become apparent to those skilled in the art upon consideration of the following description, with reference to the accompanying drawing, of which Fig. 1 is a schematic block diagram of an embodiment of the invention, Figs. 2a-2f are diagrams of the frequency spectra at various points in the system, and Fig. 3 is a circuit diagram corresponding to the block diagram of Fig. 1.

Referring to Fig. 1, a pair of directive antennas such as loops I and 3 are positioned at right angles to each other and connected to the signal inputs of balanced modulators 5 and l respectively. The control inputs of the modulators 5 and l are connected to the output circuits of balanced modulators 9 and I I, respectively, which are in turn connected to low frequency oscillators I3 and I5 respectively and to a common control oscillator l. The outputs of the modulators 5 and 'I are connected to a radio receiver I9. A

non-directive antenna 2| is also connected to the input circuit of the receiver I9. The output circuit of the receiver is connected through a band pass lter 23 to a demodulator 25, and through a band pass lter 21 to a demodulator 29 to permit monitoring of the signals picked up by the direction iinder, transducing means such as a pair of head phones 31 or the like is connected through an audio ampliiier 35 and a lter 33 to the output circuit of the receiver I9. The filter 33 is arranged to remove the modulation components introduced by the oscillators I3, I5 and Il. The outputs of the demodulators 25 and 29 are connected to orthogonally related field coils of a self-synchronous type indicating instrument 3|. 'I'he rotor coil of the device 3| is connected to the oscillator I'I.

The operation of the system is as follows: The oscillators I3, I5 and I'l are arranged to provide audio frequencies which are readily separable from speech components, such as 200, 500, and 60 cycles per second respectively. The modulator s will then provide a carrier suppressed double sideband signal (Fig. 2b) comprising the 140 and 260 cycle sidebands of a 200 cycle carrier modulated at 60 cycles. This controls the modulator 5 to produce the sidebands only of a radio frequency input modulated at and 260 cycles (Fig. 2c). For example, if the input signal is 1000 kilocycles, the output of the modulator 5 comprises the lower sidebands at 999,740 cycles and 999,860 cycles, and the upper sidebands of 1,000,140 and 1,000,260 cycles, as shown in Fig. 2c. These sidebands are combined at the input of the receiver I9 with the 1000 kilocycle carrier picked up by the antenna 2| (Fig. 2d) and produce at the receiver output (Fig. 2e) the 60 cycle sidebands of a 200 cycle carrier at 140 and 260 cycles. The sideband amplitude is proportional to the amplitude of the original 1000 kilocycle signal picked up by the loop I. The 200- cycle carrier is resupplied at the demodulator 25, which derives from the combined signals a 60-cycle voltage (Fig. 2f) likewise proportional in amplitude to the 1000 kilocycle signal.

In the same manner. a 500 cycle carrier with 60 cycle sidebands is derived from the loop 3, modulators .1 and and oscillators I5 and Il. The 200 and 500 cycle signals are separated by band pass filters 23 and 2l before demodulation at demodulators 25 and 29 respectively. The field coils of the meter 3| are thus supplied with 60 cycle voltages proportional in amplitude to the 1000 kilocycle voltages derived from the loops I and 3. The rotor of the meter is supplied with 60 cycle voltage from the oscillator Il, and rotates to align with the resultant eld of the stator windings, corresponding in direction to the azimuth of arrival of the 1000 kilocycle Wave at the antennas.

:ations in the sub-carrier amplitudes. `the'outputs l,from the modulators Vi3 and II-into 45 and 41 with push pull output circuit connece.,

tions. two control grids in phase, while the low Afrequency control input is .fed zto ithe .two .grids in push pull.

The modulators 9 and II are shown as bridge rectifier circuits, with symmetrical Vinput and output and opposed diodes 9 and 5I. The control voltage is brought in between thelcent'ers" of the input and output circuits. Copper oxide or V.similar rectiiiers may be substituted for the diodes .Auand-I.

The oscillators I3, I5 and iI -are illustrated as circuits of the Hartley type, although any preferred circuit may be used. The amplitudes of the sub-carriers generated by the oscillators I3 yand I5 are preferably made large in comparison -With the output of the oscillator Il to make the side band outputs nearly independent of vari- Similarly the modulators 5 and .TI are made large in cornparison with vthe radio frequency inputs, so that 'the outputs of the modulators 5 and I will respond only to variations'in 4the'smaller of the two inputs.

The receiver I9 is of conventional design, and includes, for example, a radio frequency amplifier, oscillator, mixer, intermediate frequency amplienand a detector, Vwhich are-not shown.

The filters 23,2'! and33 are also conventional. The demodulators .25 and.29 are illustrated as bridge circuits similar to modulators 9 `and II, with control voltages derived from `the oscillators I3 and I5 respectively. Audio amplifiers 63 and A65, stabilized by negative feedback, are provided between the outputs of the'demodulators 25 and ,2B Yand the respective coils-Eil and SS of the indicator .3 I.

Thus the invention has been described asa direct indicating direction finder. The outputs of .apair of .crossed directive antennas are differently modulated, combined andamplied together, separated according to the different modulations, Vand demodulated to provide two voltages of the same low frequency and proportional in amplitude to the respective lantenna outputs. These two voltages are used to operate a bearing indicator. v v

I claim as my invention:

l. A radio direction iinder comprising orthogonally related directive antennas, three local oscillators, modulator means arranged to .combine the outputs of one pair of said oscillators, modulator means ,arrangedto modulate the output of one of saidantennas with vthe combined output of said pair of oscillators, a second modulator means arranged to modulate the output of the other of said antennas .with the combined outputs of another .pair of said oscillators, a non- .directive antenna, means for combining the modulated outputs of said directive antennas with the output of said non-directive antenna, a radio receiver connected to-respond to the last mentioned combined Outputaiiltermeans arranged to separate the different modulation components inthe outputof said receiver, demodulators connected to 4convert said modulation vcomponents to The radio frequency input is fed .to .the

4 alternating voltages having amplitudes proportional respectively to the amplitudes of the out- `Iputs of said directive-antennasand a frequency equal to that of one of said local oscillators, and indicator means responsive to said alternating voltages and to the output of said last mentioned 4local oscillator.

2.1% radio direction finder including two difrective antennas arranged with their directivity patternsat right angles, means for doubly modulatingthe outputs of both of said antennas with one frequency common to both outputs and at otherfrequencies different for each output, means for' combining said modulated outputs, a radio receiver connected to amplify and detect said modulated and combined outputs, filter means Y for separatin'g'the components of the output of antennas.

antenna, aradioreceiver arranged to respond to said modulated and combined antenna outputs. lters connected to separate the components of the output of said receiver, and demodulators responsive to each of said components and to the output of one yof said two oscillators respectively to produce voltages of equal frequencies and of magnitudes proportional respectively to the outputs of said antennas.

4. The system as claimed in claim 2, including in addition a non-directiveantenna and means for combining the output of ksaid non-directive antenna with the doubly modulated outputs of the directive antennas.

5. In a radio direction finder employing stationary directive antennas `and a non-directive antenna, three local oscillators, means formodulating the outputs of each of two of said oscillators with the output of the third, means for modulating the .output of each .of said directive antennas with the modulated output of one of said two oscillators, means for Vcombiningvsaid modulated outputs from said directive antennas with the output of said non-directive antenna, a radio receiverarranged to respond to said modulated ,and combined. antenna outputs, filters connected to separate the components of the output of said receiver, and demodulators responsive to each ,of said components and to the output of one of .said two oscillators respectively to produce voltages of .equal frequencies and of magnitudes proportional respectively to the outputs of said directive DONALD S. BOND.

YREFERENCES CITED The following references arel of record inthe le of this patent:

UNITED STATES 'PATENTS Number Name Date 2,213,874 Wagstaffe Sept. 3, 1940 2,213,273 Earp Sept. V3, 1940 

